Exhaust gas recirculation, commonly referred to as EGR, is used to dope the air-fuel mixture introduced into the combustion chamber space for the purpose of minimizing the amount of oxides of nitrogen created during the combustion process. An EGR valve is used to control the recirculation flow, and the capabilities of electronics technology make it desirable to use an electrically controlled EGR valve. A limitation on the performance of known EGR valves resides in their inability to respond as precisely as the precise control potential that resides in the controlling electronics. This is due essentially to the fact that EGR valves are electromechanical devices.
The present invention is an answer to the need for a more responsive EGR valve which can provide more precise control of the recirculated exhaust gas. Briefly, the invention embodies a moving electromagnetic coil as the prime mover for positioning the EGR valve mechanism. The coil is disposed in a magnetic field, and control current representing desired coil position is passed through the coil. The current interacts with the magnetic field in such a way that the resultant axial force acting on the coil balances that of a mechanical bias spring force which also acts axially on the coil. The force on the coil resulting from the interaction of the electric current with the magnetic field is, for a constant magnetic field, proportional to the magnitude of the electric current so that in order to balance the bias spring force the coil will be axially positioned in proportion to the electric current.
Such an arrangement offers very significant advantages for an EGR valve. The proportionality of the coil positioning to the electric current flow through the coil can be made highly linear. The amount of axial travel which can be executed by the coil is comparatively long relative to certain other EGR valves and also relative to the axial dimension of the coil itself. Such considerations enable a more precise and responsive EGR valve to be created. By associating a position sensor with the moving coil to sense coil position, and using a signal from the position sensor as feedback to the EGR control electronics, a highly accurate and responsive EGR system can result. It is also feasible to have the electronics provide self-diagnosis of the EGR valve for giving ar alert against possible and actual EGR valve malfunction. Because the EGR is mounted in an environment where it may be subject to certain unavoidable vibrations, a further aspect of the EGR valve of this invention is the inclusion of an electromagnetic damping feature which can attenuate the influence of such vibrations on the moving coil. Still further features of the invention relate to the specific manner of implementation.
The foregoing, as well as additional features, advantages, and benefits of the invention, will be seen in the ensuing description which is accompanied by a drawing. The drawing discloses a presently preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.